1. Field
This disclosure relates to an oscillating modulator circuit useful to generate energy pulses in a circular induction accelerator, such as a Betatron.
2. Description of the Related Art
Circular induction accelerators, such as Betatrons, are magnetic devices used to accelerate electrons to relativistic energies. A high energy electron beam is extracted and directed on a suitable target, generating high energy x-rays. One application of the high energy x-rays is for logging oilfield boreholes, such as to map subsurface density and lithology.
Effective operation of a Betatron requires high, pulsed, currents and voltages to generate the magnetic field necessary for acceleration and confinement of the electrons. The Betatron device is controlled and run by several power supplies, which form the Betatron modulator. A conventional Betatron driving circuit utilizes a high voltage D.C. power supply, coupled to a pulse generating modulator circuit, which in turn drives the Betatron coils. Recapturing the pulse energy for use in subsequent pulses requires a complicated switching network and large capacitor. For example, U.S. Pat. No. 3,975,689 illustrates a network of four switches to reverse the direction of current flow from a charged capacitor to the Betatron coils. The switches tend to be lossy (power losing/heat generating) and therefore require a substantial power source to replace lost power into the system and are difficult to cool. If the temperature of the circuit components increases too much, silicon-base circuit components may fail. The circuitry may be exposed to a temperature increase due to both internal resistance and environmental exposure. The temperature at the bottom of a borehole may be 250° C. hotter than at the surface.
U.S. Pat. No. 5,077,530 to Chen discloses a Betatron driving circuit having a combination of a low voltage D.C. power supply and a high voltage excitation capacitor to drive the Betatron. Diodes and switches control pulse polarity and conduct all the current, so lossy components remain a concern. U.S. Pat. No. 5,077,530 is incorporated by reference herein in its entirety.
There remains a need for a modulator for circular induction accelerators that addresses the limitations described above and remains functional in a downhole environment.